Question on Find Function

[ghawkes]

what is the maximum number of nonlinear equations that can be solved in Mathcad with the Find function?

I am at 50 and it will not let me enter in the 51st variable.

[AlanStevens]

From the Mathcad 15 help file:

• Solve Blocks can solve systems of up to 400 variables when using the Quasi-Newton or Conjugate-Gradient solvers. The Levenberg-Marquardt solver is unconstrained, and will solve any size system. Linear systems can have up to 8192 constraints, and nonlinear systems up to 200 constraints. When you solve for complex variables, Mathcad treats the real and imaginary parts as separate variables in the algorithm, increasing the overall variable and constraint count for the problem.

Alan

[ghawkes]

When I am typing in my variables to find in the Find Function, when I try and type in my 51st comma it will not respond.

[RichardJ · Accepted solution]

It's not a limit on the number of variables, but on the number of arguments you are allowed to enter. Combine some or all of the variables into a vector.

[ghawkes]

Thanks, that fixed it to put some of the variables into one of the arguments as a vector.  I put a 7 row by 1 column vector in the 48th argument.  It solves correctly, but now I need help on how to access these values in the 48th argument.

[RichardJ]

How are you accessing the other 47?

Does this help (ignore the red; it's me being too lazy to actually define a solve block)?

[ghawkes]

I have:

F(P1,P2,P3):=Find(x1,x2,x3,x4,x5,....x46,x47,x48)   where x48 is a 7 row by 1 column vector  with succeeding rows of x48,0 x48,1 x48,2...

I access it as follows

F(P1,P2,P3)= x1

                     x2

                     x3

                      .

                      .

                     x47

                     [7,1]

where each x1, x2, x3 has a numerical value.

I'm wondering how to get at x48?  If I say F(P1,P2,P3)sub48,0 it shows the 7x1 vector.  If I subscript a 1 for the 0 it shows up as red.  How can I access each individual part?

[RichardJ]

Assign F(P1,P2,P3) to a variable rather than just evaluating it.

X:=F(P1,P2,P3)

Then you can evaluate X[48.

[RichardJ]

It is more likely a limit on the number of arguments in the function call. Try combining the variables into a vector (so instead, of x and y, x[0 and x[1, and solve for x)

[DJF]

So, I have a huge 'find' equation where combining variables into vectors would be advantageous.  Following your advice, I can replace everything with subscripted variables.  Nice, but that makes the equations awfully hard to read since everything becomes x[0, x[1 instead of Pressure, temperature or whatever.    Here's what I got to work based on your advice.

My question is if there is anyway to stick with the native variables in the equations?  Something like this is what I'm after, but never seems to work (no solution found).

Thanks, (3.1 attached)

[RichardJ]

This works in Mathcad 15:

I haven't tried in in Prime.

[DJF]

That apparently doesn't work in Prime.  (But I'm sure 4.0 will both solve that and be released on schedule this month.  )

[RichardJ]

That's a pity, because I can't think of anything else.